The present invention pertains to apparatus for conveying articles about a cyclic path and, more particularly, to apparatus for selectively varying the locus of the path.
In the manufacture of cylindrical containers of the type which have labels or other identifying indicia printed directly upon the outer surface thereof, it is necessary at some point in the manufacturing process to bring the articles into contact with a printing surface. In the manufacture of metal cans, for instance, cans are commonly placed upon a rotatable mandrel and transported along a path which passes by a printing surface. Often the printing surface comprises a rotating roller having a rubber blanket thereon, the blanket being patterned and serving to transfer a coating to the surface of a container brought in contact therewith. By allowing the mandrel to rotate freely, the surface of the container may be brought into direct frictional engagement with the printer blanket to rotate therewith and insure accurate registration of the blanket without smudging. The mandrel carrying the can subsequently travels out of registry with the printing element and eventually discharges the can onto a further conveying section for subsequent handling and processing.
It will be appreciated that the tolerances involved in the foregoing operation are extremely critical. If the path of the mandrel is too close to the printing surface excessive pressure will be brought to bear against the can, possibly distorting the printing blanket and producing a poor print upon the can. On the other hand, if the mandrel does not pass close enough to the printing element the blanket will not engage the can surface sufficiently and a "light" printing will occur in which insufficient coating material is transferred to the can to provide the desired design.
A more serious problem occurs, however, in the event of damage to a can during a preceding manufacturing process. As the cans are conveyed serially to the printing area, each is in turn engaged by a mandrel. If a can is damaged such as by indentation, crushing or tearing it will not fit satisfactorily upon the mandrel and will be discharged or rejected. Since the apparatus carrying the mandrels operates continuously, by the time a damaged can is identified and discharged it is too late to place a subsequent can upon a mandrel and the mandrel proceeds empty about its intended path. Should the empty mandrel continue about its usual path, it will engage the printing blanket. Although it bears no can, the loss in effective diameter is so slight that the mandrel will not completely clear the printing blanket and will receive a certain amount of coating material. Then, as the mandrel cycles about and receives another can the coating material deposited upon the mandrel by the printer will be transferred to the interior of the can.
Varied approaches have been attempted in order to avoid the above-described problem. With one approach the path of the mandrels is defined by a cam. The portion of the cam surface engaged when a mandrel encounters the printing blanket is separably and pivotably mounted. In the absence of a can on a given mandrel the pivotal cam section is swung to an alternate position to cause the mandrel to retract out of engagement with the printing roll. Still another approach is to provide means for sensing the absence of a can upon a given mandrel, and causing the entire printing apparatus to retract as the designated mandrel approaches. Although this approach has gained considerable popularity, the difficulties involved in causing a large, heavy printing element to rapidly advance and retract so as to skip only a predetermined one of a series of rapidly passing mandrels is apparent.
Still another prior art approach utilizes mandrels mounted upon movable arms, which are located by means of individual pneumatic cylinders. Individual cans are held in place on each mandrel by means of a vacuum system wherein a low pressure air channel is coupled to the outer surface of the mandrel for drawing a newly engaged can thereupon, and securing it in position. In the absence of a can the low pressure line continues to draw air through the mandrel, thus signifying that no can has been disposed thereon. Pressure-responsive means then operates valves coupled to the pneumatic cylinder which locates the empty mandrel, causing the mandrel to retract sufficiently to avoid engagement with the printing surface. This approach, however, requires a large number of air cylinders and associated conduits and is inordinately complex.
Accordingly, it will be understood that it would be desirable to provide an improved system for selectively conveying articles along one of two predetermined paths.
It is therefore an object of the present invention to provide improved conveying apparatus in which the path of a selected conveyed article may be rapidly varied.
It is another object of the invention to provide apparatus for selectively varying the path to be described by a moving member, including a cam assembly having a variable surface.
Still another object is to provide a shiftable cam assembly for varying the path of transported containers.
Another object is to provide means for selectively locating containers adjacent a printing surface while maintaining a substantially constant pressure therebetween.